1. Field of the Invention
This invention relates to an ophthalmological diagnosis method and an apparatus for carrying out this method, more particularly to an ophthalmological diagnosis method and apparatus whereby the eye fundus is illuminated by a beam of laser light and reflected laser light diffused by blood cells within the tissue of the eye is received and converted into an electrical signal which is analyzed to measure the state of the blood flow in the tissue of the eye fundus
2. Description of the Prior Art
Conventional optical methods for measuring the state of the blood flow in the eye fundus include those disclosed in Japanese Patent Laying-open Nos. 58(1983)-118730 and 56(1981)-49134.
In the former method the light of a He-Ne laser (632.8 nm) is used to illuminate blood vessels of the eye fundus, and the frequency shift in the light reflected from the red blood cells produced by the Doppler effect is utilized to measure the velocity of the blood flow. However, the object of this method is to examine the surface blood vessels of the fundus, not the state of the blood flow in vessels which are located deeper in the fundus tissue. Moreover, although it is generally known that the degree of penetration of the laser light into the fundus tissue depends on the wavelength of the light, at present there is no selection of a suitable wavelength that takes this characteristic into consideration.
With the latter method the fundus is illuminated by visible light with a wavelength of 550 nm to 650 nm reflected from the pigmented layer of the retina, and near-infrared light in the 700 nm to 1,000 nm range selected from light having a wavelength that is longer than 610 nm reflected back after having reached the choroid layer, and pulse waves are obtained from visible reflected light from the fundus that indicates the retinal blood flow state, and from near-infrared reflected light that indicates the choroid blood flow rate, allowing ailments of the fundus to be determined from the result of a comparison of the two pulse waves. With this method, it is not possible to evaluate one blood flow state, retinal or choroid, independently of the other. In addition, although there are a number of tissue layers in the retina, the apparatus of the method does not distinguish between layers in the blood flow evaluation.
Another method of measuring the blood flow state involves directing a laser beam of a prescribed diameter onto the fundus to produce a laser speckle pattern formed by reflected light diffused by the fundus tissue, and by analyzing movement in the speckle pattern detected as fluctuations in the intensity of the light, the state of the blood flow in the eye fundus is determined, a method in respect of which the present inventors have submitted a patent application (Appln. No. 61(1986)-38240). Again, with the said method the fundus tissue layer to be measured is not clearly defined, in addition to which consideration is not given to selection of a laser light source having a suitable wavelength. Because of this, which of the eye fundus tissue layers are being measured is unclear.